The diameter of the circle is 10.8 cm
The circumference of the circle is 33.9 cm
Step-by-step explanation:
Given that the radius of the circle is 5.4 cm
Diameter:
The diameter of the circle can be determined using the formula,

where r = 5.4
Thus, we have,

Thus, the diameter of the circle is 10.8 cm
Circumference:
The circumference of the circle can be determined using the formula,

Substituting
and
, we have,


Thus, the circumference of the circle is 33.9 cm